1. Field of the Invention
The present invention relates to a wake-up circuit, more particularly to a wake-up circuit preferred for such external switch input circuits as power-driven window switches, door modules, power-driven seat modules, etc. installed on vehicles.
2. Description of the Prior Art
Each of the external switch input circuits such as power-driven window switches, power-driven mirror switches, door modules, power-driven seat modules, etc. installed on vehicles is required to work even after the ignition key is turned off. This is why power is kept supplied to the external switch input circuit. When this circuit is kept set in a state ready to work any time, however, the power consumption increases over the capacity of the on-vehicle battery, thereby the engine of the vehicle often cannot be started.
In order to prevent such a problem, there have been proposed various types of wake-up circuits, each of which drives the subject vehicle into a low power consumption mode (sleep mode) automatically in a predetermined time after the ignition switch is turned off, thereby suppressing the power consumption, and when any one of the switches of the wake-up circuit is operated, the normal operation (wake-up) mode is restored.
Each of such the conventional wake-up circuits, as shown in the circuit diagram in FIG. 3, is configured by a controller (hereinafter, to be described as xe2x80x9cCPUxe2x80x9d) 31; a switch unit 32; pull-up means 33; and wake-up trigger signal generating means 34.
The CPU 31 is provided with a plurality of input terminals (IN1, IN2, and IN3) and a trigger signal input terminal (INT) used to receive a voltage for waking up itself from the sleep state. When a voltage entered to one of the input terminals (IN1 to IN3) drops, the CPU 31 outputs a plurality of control signals for controlling the external device (not shown). The CPU 31 goes into a predetermined state, for example, into the sleep mode, a few minutes after the ignition key is turned off. The CPU 31 is woken up by a voltage applied to the trigger signal input terminal (INT).
The switch unit 32 is provided with a plurality of switches (32a, 32b, and 32c), each of which is grounded at its one end. The other end of each of those switches (32a, 32b, and 32c) is connected to its corresponding input terminal (IN1/IN2/IN3) of the CPU 31 via a resistor (R35/R36/R37)
The pull-up means 33 connects a power supply terminal 35 to the other end of each of the switches (32a to 32c) of the switch unit 32 via pull-up resistors (R31/R32/R33) respectively so as to pull up the other end of each of the switches (32a to 32c).
The wake-up trigger signal generating means 34 is configured by a PNP switch transistor TR1 and an OR circuit (ground: 1, not ground: 0) consisting of diodes (D31, D32, and D33). The base of the transistor TR1 is connected to the anode side of the OR circuit and the emitter of the TR1 is connected to a power supply terminal 36, and the collector of the TR1 is connected to the trigger signal input terminal (INT) of the CPU 31. The cathode of the OR circuit (consisting of diodes D31, D32, and D33) is connected to the other end of each of the switches (32a to 32c) of the switch unit 32.
Because the conventional wake-up circuit is configured as described above, when any one of the switches (32a to 32c) of the switch unit 32 is operated, the switch (32a to 32c) is grounded at its one end. The voltage applied to the corresponding input terminal (IN1 to IN3) corresponding to the operated switch (32a to 32c) of the CPU 31 goes into the low level. On the other hand, the CPU 31 monitors the voltage at this input terminal (IN1 to IN3) and decides the operated switch (32a to 32c) and outputs a control signal via the output terminal (not shown) in accordance with the operated switch (32a to 32c) so as to control the subject external device installed in a vehicle.
In the case where any one of the switches (32a to 32c) of the switch unit 32 is operated while the CPU 31 is in a predetermined state, for example, in the sleep mode to be set a few minutes after the ignition key is turned off, one end of the switch (32a to 32c) is grounded. As a result, the anode side of the OR circuit composed of the diodes (D31 to D33) also takes the ground voltage, thereby the transistor TR1 is turned on. The power supply 36 thus applies a voltage to the trigger signal input terminal (INT) of the CPU 31 and the terminal (INT) is driven into the high level. At this high level of the voltage entered to the terminal (INT), the CPU 31 is restored to the normal mode and outputs control signals for controlling the subject external device installed on a vehicle, in accordance with the operated switch (32a to 32c).
Because of the configuration and the operation as described above, the CPU 31 controls the target device in accordance with the operated switch (32a to 32c) When no operation is required, the CPU 31 goes into the sleep mode so as to suppress the power consumption. When any one of the switches (32a to 32c) is operated in the sleep mode, the CPU 31 is woken up.
However, such a wake-up circuit, in which the switches (32a to 32c) of the switch unit 32 are disposed in parallel with respect to the CPU 31, is required so as to provide the same number of connection lines and the same number of input terminals (IN1 to IN3) of the CPU 31 as the number of switches (32a, 32b, and 32c) respectively. In addition, connection lines are also needed for the diodes (D31 to D33) so as to connect the wake-up trigger signal generating means 34. Consequently, the conventional wake-up circuit requires many parts and many connection lines, so that the circuit is complicated in structure.
Furthermore, because the configuration of the start-up circuit is decided by the number of switches (32a to 32c) of the switch unit 32, the wake-up circuit is not compatible with other circuits when the number of switches of the switch unit 32 differs among them. This has been an obstacle for reducing the manufacturing cost of the start-up circuit.
Furthermore, it has been difficult to increase the number of switches in the switch unit 32 without modification of the circuit configuration; for example, when another switch 32d is to be added to the switch unit 32, another connection line, another input terminal IN4, another diode D34, etc. denoted by broken lines in FIG. 3 are needed for the CPU 31. Once the start-up circuit is designed, therefore, it is very difficult to expand the circuit.
Under such circumstances, it is an object of the present invention to solve the above conventional problems and provide a wake-up circuit to be simplified in configuration, to require less parts and less connection lines, and to be configured regardless of the number of switches, thereby to be easy to increase the number of switches later.
In order to solve the above conventional problems, the wake-up circuit of the present invention comprises a controller provided with an analog voltage input terminal and a trigger signal input terminal so as to output a plurality of control signals corresponding to a value of an analog voltage entered to the analog voltage input terminal; and resistance value changing means provided with a plurality of switches and a plurality of resistors, one end of which is grounded and the other end of which is connected to the analog voltage input terminal as well as to a power source by pull-up means provided with at least a pull-up resistor, so as to change, by the switches, the resistance value between the one end and the other end, wherein a wake-up trigger signal generating means is provided between the resistance value changing means and the trigger signal input terminal, thereby the wake-up trigger signal generating means outputs a trigger signal when the voltage of the resistance value changing means changes, thereby waking up the controller.
Because the wake-up circuit is configured as described above, just one connection line is required both for the connection between the resistance value changing means and the analog voltage input terminal of the controller and for the connection between the resistance value changing means and the wake-up trigger signal generating means. The configuration of the wake-up circuit is thus simplified with use of less parts and less connection lines. In addition, because the configuration of wake-up circuit is not decided by the number of switches in the resistance value changing means, the wake-up circuit is compatible with other circuits even when the number of the switches differ among them. Therefore, the manufacturing cost of the wake-up circuit can be reduced. And, the number of switches in the resistance value changing means can be increased easily as needed.
Furthermore, in the wake-up circuit, the controller is provided with a first output terminal for outputting a high level voltage in a sleep state and a low level voltage upon receiving of the trigger signal, and the wake-up trigger signal generating means is composed of a PNP transistor at which an emitter is connected to the first output terminal, a collector is connected to the trigger signal input terminal, and a base is connected to the other end of the resistance value changing means respectively.
Because the wake-up circuit of the present invention is configured as described above, the wake-up trigger signal generating means can be composed simply of a transistor and generation of another trigger signal can be suppressed immediately when a trigger signal is detected. The power consumption of the wake-up circuit can thus be reduced.
Furthermore, the present invention has enabled the wake-up trigger signal generating means to be configured by a PNP transistor at which an emitter is connected to a power supply that outputs a high level voltage and a collector is connected to the trigger signal input terminal; and a differentiating circuit provided between the base of the PNP transistor and the other end of the resistance value changing means respectively.
Because the wake-up circuit of the present invention is configured as described above, the wake-up trigger signal generating means can be composed simply of a transistor and a differentiating circuit, and the differentiating circuit enables the trigger signal to take a low level voltage automatically. The power consumption of the wake-up circuit can thus be reduced more than ever.
Furthermore, the wake-up circuit of the present invention is configured so as to provide the pull-up means with switching means connected serially to the pull-up resistor and the controller with a second output terminal, thereby a signal output from the second output terminal turns off the switching means when the controller is in a sleep state and turns on the switching means when the controller is woken up.
Because the wake-up circuit is configured as described above, the power supply to the controller from the pull-up means is shut off in the sleep mode, so that no waste power is supplied to the controller, thereby the power consumption of the wake-up circuit can be reduced more than ever.
Furthermore, in the wake-up circuit of the present invention, the switching means is composed of a transistor at which a base is connected to the second output terminal.
Because the switching means is composed of a transistor such a way, the configuration of the switching means can be simplified.